Vitamin D (25-OH)
This blood test shows whether you have enough vitamin D for your immune system, bones, mood, and long-term health — and most Indians don't.
Vitamin D isn't really a vitamin — it's a hormone that affects over 1,000 genes. Your 25-OH level tells you whether your body has enough of it to support immune function, bone density, mood regulation, and cardiovascular health. Despite abundant sunshine, the vast majority of Indians are deficient.
Good for you if: You live in India (even if it's sunny), work indoors, have dark skin, feel fatigued or have low mood, have joint pain, or want to optimise immunity and bone health long-term.
Dive deeper into the scienceWhat is this test?
The 25-hydroxyvitamin D test (25-OH D) measures the storage form of vitamin D in your blood. When you get sun exposure or take a D3 supplement, your liver converts it to 25-OH D — which is what the test measures. This is then converted to the active form (1,25-dihydroxy D) as needed by your kidneys and other tissues.
Think of 25-OH D as your vitamin D bank account — it tells you how much reserve you have. The active form is like cash in your wallet: it changes rapidly and isn't a reliable measure of your overall status.
What your number means
| 25-OH Vitamin D | What it means | What to do |
|---|---|---|
| <12 ng/mL | Severe deficiency | High-dose loading: 60,000 IU/week for 8 weeks, then maintenance |
| 12–20 ng/mL | Deficient | 5,000–10,000 IU daily for 8–12 weeks, then retest |
| 20–30 ng/mL | Insufficient | Start 4,000–5,000 IU daily with K2; retest in 3 months |
| 30–50 ng/mL | Adequate — but suboptimal | Maintain 2,000–4,000 IU daily to reach 50+ |
| 50–80 ng/mL | Optimal — longevity target | Maintenance dose: 2,000–4,000 IU daily with K2 |
| >100 ng/mL | Upper limit — monitor | Reduce dose; check calcium levels |
Most labs call 30 ng/mL "sufficient" — that's the minimum to prevent rickets, not optimal health. Immune function, cardiovascular protection, and cancer risk reduction data consistently point to 50–80 ng/mL as the sweet spot.
How to improve it
Supplement D3 daily — not D2. Take 2,000–5,000 IU daily (higher if deficient). Always take with a fat-containing meal for absorption — vitamin D is fat-soluble.
Add K2 (MK-7) — 100–200 mcg daily. K2 directs the calcium that D3 helps absorb into bones and teeth, not arteries. D3 without K2 can contribute to arterial calcification over time.
Sun exposure — 15–20 minutes of midday sun on arms and legs helps, but isn't sufficient in Indian cities due to pollution, indoor lifestyles, and darker skin requiring more UVB exposure.
- D3 + K2 combo supplement — the most practical approach; many good Indian brands available at ₹300–600/month
- Magnesium — required for vitamin D activation; supplement 200–400 mg glycinate daily
- Reduce excess body fat — vitamin D is sequestered in fat tissue, making it less bioavailable in overweight individuals
- Retest every 3–6 months while optimising, then annually once stable at 50–80 ng/mL
Want to track your vitamin D?
eterni connects your lab results into a trajectory — so you see trends, not just a number.
Get early accessFrequently Asked Questions
What is a good vitamin D level?
Labs flag anything above 30 ng/mL as "sufficient." But from a longevity and immune perspective, the sweet spot is 50–80 ng/mL. Most vitamin D researchers personally target this range. Below 20 is frank deficiency, 20–30 is insufficient, 30–50 is adequate but suboptimal.
How much vitamin D3 should I take?
If you're deficient (<20 ng/mL), start with 5,000–10,000 IU daily for 8–12 weeks, then retest. For maintenance at 50–80 ng/mL, most people need 2,000–5,000 IU daily. Always take with K2 (MK-7) 100–200 mcg and a fat-containing meal for absorption.
Why are so many Indians vitamin D deficient?
Despite living in a sunny country, 70–90% of Indians are deficient. Darker skin requires more sun exposure, indoor lifestyles reduce UV exposure, pollution blocks UVB rays in major cities, and vegetarian diets contain almost no vitamin D. Supplementation isn't optional — it's necessary.
Can vitamin D levels be too high?
Yes, but toxicity is rare below 150 ng/mL. The main concern is hypercalcemia. Taking K2 (MK-7) alongside D3 directs calcium to bones instead of arteries. Don't exceed 10,000 IU daily without monitoring, and retest every 3–6 months when supplementing.
How it's measured
A simple blood draw — no fasting needed. Labs use immunoassay or LC-MS/MS methods. LC-MS/MS is more accurate but less common. The test costs ₹500–1,200 at major Indian labs. Morning sampling is preferred but not strictly required. Results are reported in ng/mL (some labs use nmol/L — multiply ng/mL by 2.5 to convert).
Clinical ranges vs optimal ranges
The Institute of Medicine (IOM) defined sufficiency as 20 ng/mL — enough to prevent rickets and osteomalacia. The Endocrine Society bumped it to 30 ng/mL. Neither threshold was designed for optimal immune function or cardiovascular protection.
Large observational studies (NHANES, UK Biobank) show the lowest all-cause mortality at 40–60 ng/mL. Immune function studies show optimal T-cell activation at 40–60 ng/mL. The 50–80 ng/mL target balances these findings with a safety margin below potential toxicity.
India-specific considerations
India has a vitamin D deficiency pandemic — 70–90% of the population across all age groups and regions is deficient. Contributing factors: melanin-rich skin needs 3–5× more UVB exposure, urban pollution blocks UVB wavelengths, indoor work cultures, and vegetarian diets (dietary vitamin D comes primarily from fatty fish and fortified dairy).
The standard Indian diet provides roughly 100–200 IU of vitamin D daily — far below the 2,000–4,000 IU needed for optimal levels. Supplementation is essentially mandatory for most Indians.
Connected supplements
- Vitamin D3 — cholecalciferol; the preferred supplemental form (not D2/ergocalciferol)
- Vitamin K2 (MK-7) — directs D3-mobilised calcium to bones; prevents arterial calcification
- Magnesium — required cofactor for D3 activation; deficiency impairs vitamin D metabolism
- Calcium — D3 enhances calcium absorption; ensure adequate intake but don't oversupplement
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eterni connects your lab results, supplements, and retests — so you can see the trajectory, not just a snapshot.
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